package edu.princeton.cs.algs4;

import edu.princeton.cs.stdlib.In;
import edu.princeton.cs.stdlib.StdOut;

/*************************************************************************
 * Compilation: javac BreadthFirstDirectedPaths.java Execution: java
 * BreadthFirstDirectedPaths V E Dependencies: Digraph.java Queue.java
 * Stack.java
 * 
 * Run breadth first search on a digraph. Runs in O(E + V) time.
 * 
 * % java BreadthFirstDirectedPaths tinyDG.txt 3 3 to 0 (2): 3->2->0 3 to 1 (3):
 * 3->2->0->1 3 to 2 (1): 3->2 3 to 3 (0): 3 3 to 4 (2): 3->5->4 3 to 5 (1):
 * 3->5 3 to 6 (-): not connected 3 to 7 (-): not connected 3 to 8 (-): not
 * connected 3 to 9 (-): not connected 3 to 10 (-): not connected 3 to 11 (-):
 * not connected 3 to 12 (-): not connected
 * 
 *************************************************************************/

public class BreadthFirstDirectedPaths {
	private static final int INFINITY = Integer.MAX_VALUE;
	private boolean[] marked; // marked[v] = is there an s->v path?
	private int[] edgeTo; // edgeTo[v] = last edge on shortest s->v path
	private int[] distTo; // distTo[v] = length of shortest s->v path
	private final int s; // the source

	public BreadthFirstDirectedPaths(Digraph G, int s) {
		marked = new boolean[G.V()];
		distTo = new int[G.V()];
		edgeTo = new int[G.V()];
		for (int v = 0; v < G.V(); v++)
			distTo[v] = INFINITY;
		this.s = s;
		bfs(G, s);
	}

	private void bfs(Digraph G, int s) {
		Queue<Integer> q = new Queue<Integer>();
		marked[s] = true;
		distTo[s] = 0;
		q.enqueue(s);
		while (!q.isEmpty()) {
			int v = q.dequeue();
			for (int w : G.adj(v)) {
				if (!marked[w]) {
					edgeTo[w] = v;
					distTo[w] = distTo[v] + 1;
					marked[w] = true;
					q.enqueue(w);
				}
			}
		}
	}

	// length of shortest path from s to v
	public int distTo(int v) {
		return distTo[v];
	}

	// is there a directed path from s to v?
	public boolean hasPathTo(int v) {
		return marked[v];
	}

	// return shortest path from s to v; null if no such path
	public Iterable<Integer> pathTo(int v) {
		if (!hasPathTo(v))
			return null;
		Stack<Integer> path = new Stack<Integer>();
		for (int x = v; x != s; x = edgeTo[x])
			path.push(x);
		path.push(s);
		return path;
	}

	public static void main(String[] args) {
		In in = new In(args[0]);
		Digraph G = new Digraph(in);
		// StdOut.println(G);

		int s = Integer.parseInt(args[1]);
		BreadthFirstDirectedPaths bfs = new BreadthFirstDirectedPaths(G, s);

		for (int v = 0; v < G.V(); v++) {
			if (bfs.hasPathTo(v)) {
				StdOut.printf("%d to %d (%d):  ", s, v, bfs.distTo(v));
				for (int x : bfs.pathTo(v)) {
					if (x == s)
						StdOut.print(x);
					else
						StdOut.print("->" + x);
				}
				StdOut.println();
			}

			else {
				StdOut.printf("%d to %d (-):  not connected\n", s, v);
			}

		}
	}

}
